Hot runner injection molding and molds have been available and successfully employed since the 1950's. Of course during this period, the plastic materials molded have been those commonly accepted as suitable for injection molding processes. For example polyethylene, polypropylene, blends of pylyethylene/polypropylene, polycarbonates and others well known in the molding art. These materials had and have very comparable characteristics (i.e. melt ranges, flow conditions, etc.) all which lend themselves to the injection molding process. Plastic materials engineering has however made significant advances since the mid 1970's. Whole new classes of polymers known as engineering, high-temperature and high-strength plastics, elastomers and liquid crystal polymers, have appeared and created whole new product categories. However, economical processing of these materials is a necessary adjunct to the successful adoption of them for use in broad product fields or categories.
Therefore, it was expected that injection molders would begin experimentation with these new materials and seek to develop successful processes and apparatus to accomplish these uses.